Browsing by Subject "Magnetic nanoparticles"

Now showing 1 - 10 of 10

Open Access
Coded scenes for fast system calibration in magnetic particle imaging
(IEEE, 2018) Ilbey, S.; Top, C. B.; Güngör, A.; Sarıtaş, Emine Ülkü; Güven, E.
Magnetic nanoparticle (MNP) agents have a wide range of clinical application areas for both imaging and therapy. MNP distribution inside the body can be imaged using Magnetic Particle Imaging (MPI). For MPI image reconstruction with the system function matrix (SFM) approach, a calibration scan is necessary, in which a single MNP sample is placed and scanned inside the full field of view (FOV), which is a very time consuming task. In this study, we propose the use of coded scenes that include MNP samples at multiple positions inside the FOV, and reconstruct the SFM using compressed sensing techniques. We used simulations to analyze the effect of number of coded scenes on the image quality, and compare the results with standard sparse reconstruction using single MNP sample scan. The results show that with the proposed method, the required number of measurements is decreased substantially, enabling a fast system calibration procedure.
Open Access
Low drive field amplitude for improved image resolution in magnetic particle imaging
(Wiley-Blackwell Publishing, Inc., 2016) Croft, L. R.; Goodwill, P. W.; Konkle, J. J.; Arami, H.; Price, D. A.; Li, A. X.; Saritas, E. U.; Conolly, S. M.
Purpose: Magnetic particle imaging (MPI) is a new imaging technology that directly detects superparamagnetic iron oxide nanoparticles. The technique has potential medical applications in angiography, cell tracking, and cancer detection. In this paper, the authors explore how nanoparticle relaxation affects image resolution. Historically, researchers have analyzed nanoparticle behavior by studying the time constant of the nanoparticle physical rotation. In contrast, in this paper, the authors focus instead on how the time constant of nanoparticle rotation affects the final image resolution, and this reveals nonobvious conclusions for tailoring MPI imaging parameters for optimal spatial resolution. Methods: The authors first extend x-space systems theory to include nanoparticle relaxation. The authors then measure the spatial resolution and relative signal levels in an MPI relaxometer and a 3D MPI imager at multiple drive field amplitudes and frequencies. Finally, these image measurements are used to estimate relaxation times and nanoparticle phase lags. Results: The authors demonstrate that spatial resolution, as measured by full-width at half-maximum, improves at lower drive field amplitudes. The authors further determine that relaxation in MPI can be approximated as a frequency-independent phase lag. These results enable the authors to accurately predict MPI resolution and sensitivity across a wide range of drive field amplitudes and frequencies. Conclusions: To balance resolution, signal-to-noise ratio, specific absorption rate, and magnetostimulation requirements, the drive field can be a low amplitude and high frequency. Continued research into how the MPI drive field affects relaxation and its adverse effects will be crucial for developing new nanoparticles tailored to the unique physics of MPI. Moreover, this theory informs researchers how to design scanning sequences to minimize relaxation-induced blurring for better spatial resolution or to exploit relaxation-induced blurring for MPI with molecular contrast.
Open Access
Magnetic Particle Imaging (MPI) for NMR and MRI researchers
(Elsevier, 2013) Sarıtaş, Emine Ülkü
Magnetic Particle Imaging (MPI) is a new tracer imaging modality that is gaining significant interest from NMR and MRI researchers. While the physics of MPI differ substantially from MRI, it employs hardware and imaging concepts that are familiar to MRI researchers, such as magnetic excitation and detection, pulse sequences, and relaxation effects. Furthermore, MPI employs the same superparamagnetic iron oxide (SPIO) contrast agents that are sometimes used for MR angiography and are often used for MRI cell tracking studies. These SPIOs are much safer for humans than iodine or gadolinium, especially for Chronic Kidney Disease (CKD) patients. The weak kidneys of CKD patients cannot safely excrete iodine or gadolinium, leading to increased morbidity and mortality after iodinated X-ray or CT angiograms, or after gadolinium-MRA studies. Iron oxides, on the other hand, are processed in the liver, and have been shown to be safe even for CKD patients. Unlike the “black blood” contrast generated by SPIOs in MRI due to increased dephasing, SPIOs in MPI generate positive, “bright blood” contrast. With this ideal contrast, even prototype MPI scanners can already achieve fast, high-sensitivity, and high-contrast angiograms with millimeter-scale resolutions in phantoms and in animals. Moreover, MPI shows great potential for an exciting array of applications, including stem cell tracking in vivo, first-pass contrast studies to diagnose or stage cancer, and inflammation imaging in vivo. So far, only a handful of prototype small-animal MPI scanners have been constructed worldwide. Hence, MPI is open to great advances, especially in hardware, pulse sequence, and nanoparticle improvements, with the potential to revolutionize the biomedical imaging field.
Open Access
Probing viscosity via relaxation in magnetic particle imaging
(2017-01) Ütkür, Mustafa
Magnetic Particle Imaging (MPI) is a high-contrast imaging modality with applications such as angiography, stem cell tracking, and cancer imaging. In recent years, MPI was shown to be a potential functional imaging modality through \color MPI" techniques, where responses from different nanoparticles can be distinguished. These techniques can be extended to differentiate environmental conditions or states such as different viscosities. Increased viscosity in vivo was shown to be related with various diseases such as hypertension, atherosclerosis, and cancer. Through color MPI techniques, MPI shows a great promise for mapping viscosity and for helping in the diagnosis of these important diseases. This thesis demonstrates the capability of MPI to map viscosities through an estimation of relaxation time constant of nanoparticles. This capability is verified through an extensive experimental work with a magnetic particle spectrometer (MPS) setup that is custom designed. These experiments are conducted for the biologically important viscosity range between 0.89 mPa.s and 15.33 mPa.s, at four different frequencies (between 250 Hz and 10.8 kHz) and at three different field amplitudes (between 5 mT and 15 mT). The results demonstrate MPI's viscosity mapping capability in a biological range.
Open Access
Reclamation of used lubricating oils using magnetic nanoparticles and caustic soda
(2017-06) Ashirov, Timur
Oils are one of the mostly used lubricants in industry. Chemical oxidation, however, causes depletion of additive materials i.e. antioxidants in lubricants and their usage life time shortens. This causes varnish and sludge problems and leaves behind tons of used oil that loses its functionality. It is reported that more than 600 tons of lubricating oil can be reclaimed from 1000 tons of used oil. One of the reclamation methods is caustic extraction, and has been known for more than 3 decades. Although caustic extraction has a very high potential because of its economic considerations, this method is not fully understood due to lack of research. We have revealed that opposite to the common belief, oxidized oils (used oils) have ester groups in contrary to carboxylic acids. Magnetic nanoparticles (Fe3O4) can be used as a catalyst for hydrolysis of various esters. We have investigated the effect and mechanism of caustic extraction in combination with magnetic iron oxide nanoparticles. Using sodium hydroxide, breaks ester bonds by forming carboxylate salts and alcohols. These carboxylate salts are transferred into water and can be removed by water. Formed alcohol groups can be trapped by drying agents like MgSO4. Further purification of reclaimed oils can be achieved using hexane or similar low molecular weight and inexpensive solvents. According to our results, properties of recovered base oils mostly compete with petroleum based and ester-based synthetic base oil properties.
Open Access
Relaxation-based viscosity mapping for magnetic particle imaging
(Institute of Physics Publishing, 2017) Utkur, Mustafa; Muslu, Yavuz; Sarıtaş, Emine Ülkü
Magnetic particle imaging (MPI) has been shown to provide remarkable contrast for imaging applications such as angiography, stem cell tracking, and cancer imaging. Recently, there is growing interest in the functional imaging capabilities of MPI, where 'color MPI' techniques have explored separating different nanoparticles, which could potentially be used to distinguish nanoparticles in different states or environments. Viscosity mapping is a promising functional imaging application for MPI, as increased viscosity levels in vivo have been associated with numerous diseases such as hypertension, atherosclerosis, and cancer. In this work, we propose a viscosity mapping technique for MPI through the estimation of the relaxation time constant of the nanoparticles. Importantly, the proposed time constant estimation scheme does not require any prior information regarding the nanoparticles. We validate this method with extensive experiments in an in-house magnetic particle spectroscopy (MPS) setup at four different frequencies (between 250 Hz and 10.8 kHz) and at three different field strengths (between 5 mT and 15 mT) for viscosities ranging between 0.89 mPa • s-15.33 mPa • s. Our results demonstrate the viscosity mapping ability of MPI in the biologically relevant viscosity range.
Open Access
Selection field induced artifacts in magnetic particle imaging and a novel framework for nanoparticle characterization
(2020-10) Yağız, Ecrin
Magnetic particle imaging (MPI) is a recent imaging modality that uses nonlinear magnetization curves of the superparamagnetic iron oxides. One of the main assumptions in MPI is that the selection field changes linearly with respect to the position, whereas in practice it deviates from its ideal linearity in regions away from the center of the scanner. The first part of this thesis demonstrates that unaccounted non-linearity of the selection field causes warping in the image reconstructed with a standard x-space approach. Unwarping algorithms can be applied to effectively address this issue, once the displacement map acting on the reconstructed image is determined. The unwarped image accurately represents the locations of nanoparticles, albeit with a resolution loss in regions away from the center of the scanner due to the degradation in selection field gradients. In MPI, the relaxation behavior of the nanoparticles can also be used to infer about nanoparticle characteristics or the local environment properties, such as viscosity and temperature. As the nanoparticle signal also changes with drive field (DF) parameters, one potential problem for quantitative mapping applications is the optimization of these parameters. In the second part of this thesis, a novel accelerated framework is proposed for characterizing the unique response of a nanoparticle under different environmental settings. The proposed technique, called “Magnetic Particle Fingerprinting” (MPF), rapidly sweeps a wide range of DF parameters, mapping the unique relaxation fingerprint of a sample. This technique can enable simultaneous mapping of several parameters (e.g., viscosity, temperature, nanoparticle type, etc.) with significantly reduced scan time.
Open Access
Signal prediction for magnetic particle imaging using a model-based dictionary approach
(2023-07) Alpman, Aslı
Magnetic particle imaging (MPI) is a tracer-based medical imaging technique that enables quantification and spatial mapping of magnetic nanoparticle (MNP) distribution. The magnetization response of MNPs depends on both experimental conditions such as drive field (DF) settings and viscosity of the medium, and the magnetic parameters such as magnetic core diameter, hydrodynamic diameter, and magnetic anisotropy constant. A comprehensive understanding of the magnetization response of MNPs can facilitate the optimization of DF and MNP type for a given MPI application. This thesis proposes a calibration-free algorithm using model-based dictionaries for MNP signal prediction at untested experimental conditions. The proposed algorithm also incorporates non-model-based dynamics by modeling them as a linear time-invariant system. These dynamics include the system response of the measurement setup as well as the magnetization dynamics not accounted for by the employed coupled Brown-N´eel rotation model, such as dipolar interactions and non-uniaxial magnetic anisotropy. The proposed iterative calibration-free algorithm simultaneously estimates the dictionary weights and the transfer functions due to non-model based dynamics. Experiments on in-house magnetic particle spectrometer (MPS) setup demonstrate that the pro-posed algorithm successfully predicts the MNP signals at untested viscosities within the biologically relevant range, as well as at untested DF settings.
Open Access
Simultaneous temperature and viscosity estimation capability via magnetic nanoparticle relaxation
(Wiley-Blackwell Publishing, Inc., 2022-04) Utkur, Mustafa; Sarıtaş, Emine Ülkü
Purpose: Magnetic particle imaging (MPI) is emerging as a highly promising imaging modality. Magnetic nanoparticles (MNPs) are used as imaging tracers in MPI, and their relaxation behavior provides the foundation for its functional imaging capability. Since MNPs are also utilized in magnetic fluid hyperthermia (MFH) and MPI enables localized MFH, temperature mapping arises as an important application area of MPI. To achieve accurate temperature estimations, however, one must also take into account the confounding effects of viscosity on the MPI signal. In this work, we analyze the effects of temperature and viscosity on MNP relaxation and determine temperature and viscosity sensitivities of relaxation time constant estimations via TAURUS (TAU estimation via Recovery of Underlying mirror Symmetry) at a wide range of operating points to empower simultaneous mapping of these two parameters. Methods: A total of 15 samples were prepared to reach four target viscosity levels (0.9–3.6 mPa (Formula presented.) s) at five different temperatures (25–45 (Formula presented.) C). Experiments were performed on a magnetic particle spectrometer (MPS) setup at 60 different operating points at drive field amplitudes ranging between 5 and 25 mT and frequencies ranging between 1 and 7 kHz. To enable these extensive experiments, an in-house arbitrary-waveform MPS setup with temperature-controlled heating capability was developed. The operating points were divided into four groups with comparable signal levels to maximize signal gain during rapid signal acquisition. The relaxation time constants were estimated via TAURUS, by restoring the underlying mirror symmetry property of the positive and negative half cycles of the time-domain MNP response. The relative time constants with respect to the drive field period, (Formula presented.), were computed to enable quantitative comparison across different operating points. At each operating point, a linear fit was performed to (Formula presented.) as a function of each functional parameter (i.e., temperature or viscosity). The slopes of these linear fits were utilized to compute the temperature and viscosity sensitivities of TAURUS. Results: Except for outlier behaviors at 1 kHz, the following global trends were observed: (Formula presented.) decreases with drive field amplitude, increases with drive field frequency, decreases with temperature, and increases with viscosity. The temperature sensitivity varies slowly across the operating points and reaches a maximum value of 1.18%/ (Formula presented.) C. In contrast, viscosity sensitivity is high at low frequencies around 1 kHz with a maximum value of 13.4%/(mPa (Formula presented.) s) but rapidly falls after 3 kHz. These results suggest that the simultaneous estimation of temperature and viscosity can be achieved by performing measurements at two different drive field settings that provide complementary temperature/viscosity sensitivities. Alternatively, temperature estimation alone can be achieved with a single measurement at drive field frequencies above 3 kHz, where viscosity sensitivity is minimized. Conclusions: This work demonstrates highly promising temperature and viscosity sensitivities for TAURUS, highlighting its potential for simultaneous estimation of these two environmental parameters via MNP relaxation. The findings of this work reveal the potential of a hybrid MPI–MFH system for real-time monitored and localized thermal ablation treatment of cancer.
Open Access
Tomographic field free line magnetic particle imaging with an open-sided scanner configuration
(IEEE, 2020) Top, C. B.; Güngör, Alper
Superparamagnetic iron oxide nanoparticles (SPIONs) have a high potential for use in clinical diagnostic and therapeutic applications. In vivo distribution of SPIONs can be imaged with the Magnetic Particle Imaging (MPI) method, which uses an inhomogeneous magnetic field with a field free region (FFR). The spatial distribution of the SPIONs are obtained by scanning the FFR inside the field of view (FOV) and sensing SPION related magnetic field disturbance. MPI magnets can be configured to generate a field free point (FFP), or a field free line (FFL) to scan the FOV. FFL scanners provide more sensitivity, and are also more suitable for scanning large regions compared to FFP scanners. Interventional procedures will benefit greatlyfrom FFL based open magnet configurations. Here, we present the first open-sided MPI system that can electronically scan the FOV with an FFL to generate tomographic MPI images. Magnetic field measurements show that FFL can be rotated electronically in the horizontal plane and translated in three dimensions to generate 3D MPI images. Using the developed scanner, we obtained 2D images of dot and cylinder phantoms with varying iron concentrations between 11 μg/ml and 770 μg/ml. We used a measurement based system matrix image reconstruction method that minimizes 11-norm and total variation in the images. Furthermore, we present 2D imaging results of two 4 mm-diameter vessel phantoms with 0% and 75% stenosis. The experiments show high quality imaging results with a resolution down to 2.5 mm for a relatively low gradient field of 0.6 T/m.